Field of the Invention
This invention relates to electrically operated valve actuators, and more particularly to a fail-safe valve actuator.
Description of the Prior Art
In the petroleum and related industries, valve actuators are employed for controlling the flow of liquid from one location to another, for example in fuel feed lines of electrical power generation stations and in the transportation of both refined and crude petroleum products. In such installations, it is sometimes necessary to terminate flow in certain emergencies, such as the loss of electrical power, in order to prevent loss of fuel and/or the undesirable effects of contamination or pollution.
One type of actuator which has found advantageous use in the aforementioned application is disclosed by Malcolm D. Clark in his U.S. Pat. 3,572,163, granted Mar. 23, 1971 and assigned to Raymond Control Systems, Inc. Although this valve actuator has proven advantageous in many applications, it primarily depends upon the availability and integrity of electrical power supply for operation. In recognizing that outages occur, and that it may be necessary to operate a valve during a power failure, Clark provided his actuators with means for electrically disconnecting the electric motor and mechanically disengaging the motor from the output shaft connected to the valve, and means for manually operating the actuator. Although service personnel are alerted of the necessity for manual operation of the valve by means of monitoring devices, loss of fuel and/or pollution could occur between the time a service man is alerted to operate the valve and the time that the valve is actually manually operated.